A number and variety of sealing means and materials have been developed in response to the demand for sealing means for closing vessels and for compartmentalizing them liquid and gas tightly. Heretofore, the best septa for these purposes have not been reliably gas tight and have not been self closing after a few or several syringe punctures. Attempts to overcome these shortcomings have led to a development of composite bodies of plastic materials in laminar form with a cover of metal foil intended to make the assembly gas tight. Bonding of the laminae, however, is still an important problem, and so is maintaining the sealing integrity of the metal foil by preventing wrinkling, crinkling, bubbling and cracking of the foil as it is secured to a flexible and resilient body.